A method of operating a well using an electric pump with a variable frequency drive (as disclosed in Russian patent no. RF 2426867) is known. That method is based on continuously operating the pump, and includes starting the pump with a defined process rate, changing the supply voltage frequency when the pump reaches a defined frequency in a stationary mode, with acceleration in case of a pump-off condition, and providing a supply of liquid by pump in the stationary mode at the defined frequency, to compensate for instability in the feed and maintain a stable balance between liquid drawn from the well and fluid inflow from the formation surrounding the well. Periodically, cycles are performed consisting of alternating; pumping, pumping off fluid, and accumulating fluid in the well. Pumping off is accomplished by modulating the frequency in a range of values corresponding to the parameters of maintaining a pump delivery rate with subsequent maintenance of the maximum frequency at which the pump does not resume delivery. In the inflow phase of fluid into the well, in the current cycle they modulate the frequency of the supply voltage of the electric pump in the frequency range corresponding to the change during fluid inflow parameters of pump in when delivery is stopped and resumed. During the inflow of fluid, the intake pressure of the pump reaches the defined value, and they resume delivery of the, fluid by pump, After that the cycle is repeated, and when in the current cycle the frequency of resuming the delivery does not exceed the defined frequency, the pump is switched into stationary mode. This differs from the present invention because, in the case of pump starvation, when it is brought to the defined frequency of the stationary mode during the defined time intervals of resuming and stopping of pump delivery, the additional frequency modulation for resuming fluid delivery is performed. Additional modulation is performed before pumping is resumed, which is performed at the additional frequency with a defined deviation from the frequency achieved before additional modulation of the pump's starvation frequency. After that it is necessary to continue bringing the pump to defined frequency of stationary mode with defined process rate of stabilization of the well.
In this method, modulating the frequency is performed for bringing the pump to a defined stationary frequency.
There is a known method of well exploitation using an electric submersible pump with a variable frequency drive (as discussed in Russian patent no. RF 2421605), which is used to stabilize wells equipped with an electric submersible pump (ESP) after a workover which implies changing the frequency of the electric motor supply voltage depending on the watercut of the well fluid.
However in this method the frequency of the supply voltage is changed only when the well is in pumpdown mode.
A method is for pumping low-flow rate wells using an electric pump with a variable frequency drive and device (Patent RU 2119578), based on periodic repeating cycles, including starting the pump with an increasing supply voltage frequency, operating the pump at the defined frequency, and after reaching a defined pressure in the tubing string at that frequency, the supply voltage frequency is reduced until the pump stops delivering fluid. Subsequently, a maximum frequency is maintained that ensures inflow from the surrounding formation and the pump does not resume delivery. After reaching defined pressure at the pump intake due to the inflow, the cycle is repeated and pump delivery is resumed by increasing its frequency.
The known method has the following disadvantages:
Sophisticated structures are needed to implement the method, namely, using additional downhole equipment such as temperature and pressure measuring systems installed under the downhole motor, which increases the cost of the method and prevents its application in areas of high temperature formation fluid (i.e., above 90° C.), due to the downhole electronics failing.
Thus the method is suitable only for low production wells.
Additionally, the pump shut off time is determined solely on the power and bench test characteristics of the pump, which causes significant errors, because testing is performed on fluid characteristics that do not match the fluid characteristics in each individual well.